1. Field of the Invention
The present invention relates to a drive assembly for an electric motor and, more particularly, to a combination brake and clutch assembly for electric motors.
2. Description of the Prior Art
It is well known in the art of various devices, such as closures, which are operated by way of electric motors to provide the electric motor with a brake to prevent manual operation of the closure by unauthorized personnel or the like.
For instance, Canadian Patent No. 1,165,785 issued on Apr. 17, 1984 discloses a typical brake for electric motors used frequently in the art.
More particularly, with reference to FIGS. 1 and 2 of the aforementioned Canadian Patent, a door operator 10 comprises an electric motor 11 adapted to drive a V-belt pulley 12 mounted on the motor shaft which in turn drives, by way of a V-belt 15, a larger V-belt pulley 13 provided on an intermediate shaft 14. A chain drive 16 connects the intermediate shaft 14 to an intermediate sprocket 17 mounted on shaft 18 while a further chain drive 19 joins the shaft 18 to a drive sprocket 20 which operates an output shaft 21. The output shaft 21 which is supported on two pillow blocks 22 mounted on frame members 23 is adapted to open and close a closure, such as a garage door or the like. A control box 25 is mounted on the frame members 23.
More importantly with respect to the present invention, the motor shaft is provided with a brake 27 which is operated by a lever mechanism 28. The lever mechanism 28 is connected to an arm 29 rotated by a shaft 30 entering the control box 25. A solenoid 42 operates in such a way so as to rotate the brake shaft 30, whereby when the electric motor 11 is powered to go in either direction the solenoid 42 is energized thereby causing the brake 27 to be released.
Therefore, when the motor 11 is not operating, the solenoid 42 ensures that the two-jawed clamp-type brake 27 grips firmly the motor shaft to prevent the same from rotating, whereby the equipment, such as a closure, connected to the motor shaft and thus normally operated by the electric motor 11 cannot be manually displaced. Obviously, in the aforementioned Canadian Patent, this tamper-proof feature can be by-passed as there is provided a manual release lever 31 on the other side of the door operator 10 from the brake 27 which comprises a linkage (not shown) for allowing the brake 27 to be manually released when it is necessary to operate the door operator 10 manually. Applicant wishes herein only to illustrate a typical brake mechanism which is used on a motor shaft for preventing the manual rotation of the motor when the latter is not energized and thus also the operation of the closure, or the like, connected thereto.
Accordingly, the typical braking system for electric motors requires a solenoid which, after some use, tends to fail. Furthermore, it would also be preferable to incorporate a clutch mechanism to protect the motor in the event that the equipment operated by the motor (such as a closure) does not work properly and produces a torque against the rotation of the motor shaft which could cause the speed of the latter to be reduced or even stopped.